class Solution {
public:
    int uniquePaths(int m, int n) {
        // dp[i][j] = dp[i - 1][j] + dp[i][j - 1];

        vector<vector<int>> dp(m + 1, vector<int>(n + 1));
        dp[0][1] = 1;
        for(int i = 1; i <= m; i++)
            for(int j = 1; j <= n; j++)
                dp[i][j] = dp[i - 1][j] + dp[i][j - 1];
        return dp[m][n];
    }
};

class Solution {
public:
    int uniquePathsWithObstacles(vector<vector<int>>& ob) {
        // 状态表示 到达 ij位置是一共有多少方案
        // 网格中有1，不填表 obstacleGrid[i][j] != 1
        // barrier
        // 状态方程：dp[i][j] = dp[i - 1][j] + dp[i][j - 1];
        int m = ob.size();
        int n = ob[0].size();
        vector<vector<int>> dp(m + 1, vector<int>(n + 1));
        dp[0][1] = 1;
        for(int i = 1; i <= m; i++)
            for(int j = 1; j <= n; j++)
                if(ob[i - 1][j - 1] == 0)
                    dp[i][j] = dp[i - 1][j] + dp[i][j - 1];
        return dp[m][n];
    }
};